1. Field of the Invention
The present invention deals with a process of producing olefin polymers in the presence of an olefin polymerisation catalyst. More specifically, the present invention deals with a method of transferring a solid polymerisation catalyst component into the polymerisation reactor. In particular, the solid catalyst component can be metered into the reactor with good accuracy without damaging the properties of the catalyst.
2. Description of Related Art
WO 9216747 discloses a device and a method for metering a viscous mixture of a wax and a polymerisation catalyst into the polymerisation reactor by using a valveless piston pump. It was disclosed that the catalyst—wax mixture having a viscosity of from 0.1 to 500000 mPa·s could be used. However, it was reported that the catalyst was mixed with a solution of polyethylene wax and liquid poly-alpha-olefin, where the viscosity of the polyethylene wax—poly-alpha-olefin mixture was 4500 mPa·s in the feed conditions.
WO 00/47638 discloses a method for polymerising olefins in the presence of a preactivated catalyst. The catalyst was mixed with oil and wax and metered into the polymerisation reactor by using a device disclosed in WO 9216747. The viscosity of the mixture was from 1 to 15 Pas, preferably from 4 to 10 Pas.
DE 248634 discloses a valveless piston pump capable for pumping viscous materials.
WO 01/05845 discloses a method for polymerising olefins in a fluidised bed gas phase reactor, where a solid catalyst component was mixed with oil having a viscosity of at least 50 mPa·s, preferably greater than 100 mPa·s but no greater than 5000 mPa·s. The catalyst slurry was mixed with aluminium alkyl compounds and passed through a static mixer, after which it was introduced into a fluidised bed polymerisation reactor.
EP 459218 discloses a shot-injector type of catalyst feeder, where catalyst slurry is allowed to settle so that the catalyst fills a bore of a feeder valve. When the valve turns the shot of settled catalyst is injected into the polymerisation reactor.
Solid catalyst components having small particle size, low density or high porosity have a tendency of settling slowly in a diluent. Therefore, if such catalysts are fed by using shot injector type of feeders as disclosed in EP 459218, the feed capacity is limited due to the low content of solid catalyst in the feed shots. This problem can be solved by mixing the catalyst into a viscous wax mixture, but the use of additional and viscous components requires special equipment.